China's Space Program Thread II

[Quickie]

Yeah but how? Where did you get exhaust velocity from when we don't have the delta-v for the SRM, and vice versa?

Unless there's a different formula I'm not aware of, burn time alone doesn't give you enough metrics as you can't really calculate with any "accuracy" the mass flow rate without the volume of the canister or the density of the propellant itself.

This is how the Specific Impulse is defined:

For all vehicles, specific impulse (impulse per unit weight-on-Earth of propellant) in seconds can be defined by the following equation:

where:

• 
  is the thrust obtained from the engine (
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  or
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  ),
• 
  is the
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  , which is nominally the gravity at Earth's surface (m/s2 or ft/s2),
• 
  is the specific impulse measured (seconds),
• 
  is the
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  of the expended propellant (kg/s or
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  /s)

Basically, I'm making an assumption of a constant fuel-burning rate and constant thrust.
Exhaust velocity can be calculated when the Isp is known.
.

 

[Blitzo]

Too much frequent changes. They are really just following whatever the US is up to by now.

That's a hell of a hot take there.

 

[taxiya]

Like I said HTPB, NEPE etc are binding processes. They're just different biding agents to the solid fuel mix which comes in powder form, and they only make up like 8-10% of the total with the majority being ammonium perchlorate. It's what gives the fuel mix the plasticity to turn into a useable solid fuel. These are essentially plastic explosives a la C-4 repurposed as propellants via controlled explosions.

There's not only one type of HTPB, itself a mixture that can be re-formulated into many varieties to suit the specific needs and parameters of a given fuel mix. The fact HTPB has been around for a long time is irrelevant as the polybutadiene base continues to be refined depending on use case.

PBAN is the same PB base re-tweaked for the SSSRB during the Space Shuttle era. NEPE is a different mixture entirely that primarily uses nitroglycerin as a base that supposedly squeezes more performance from the overall fuel mix as it doesn't require as much binding agent and plasticiser, so that a higher proportion is taken up by the primary oxidiser which is still ammonium perchlorate. The famous one being NEPE-75 inside the Trident II that has 75% solids, hence the name.

As I'm not a chemical engineer, please don't make me explain how these chemicals and mixtures differ in specific properties. All I know from my reading of the subject is that China has been using HTPB as the primarily solid fuel for missile boosters since the DF-21 days. Plenty of research has been done in China on NEPE, for sure. There're rumours DF-41 uses NEPE but these are still rumours.

As I said HTPB isn't one type of fuel as it continually gets refined and repurposed. Best example that's relevant to this topic is again the SRBs from the Ariane series, from the P241 EAP on Ariane 5 to the new P120 EAP on Ariane 6 where they all utilise AP/HTPB as fuel, and these SRBs are able to achieve higher specific impulses and fuel efficiencies over the SSSRB which uses a "newer" fuel that is PBAN-based.


As for N15, all I got from your quotes is that it having an "equivalent performance to NEPE" =/= it being NEPE.

Here's a research paper published by a team from several Chinese institutes, amongst them notably were the PLA Army Engineering University and the 713 Institute of CSIC i.e. China Shipbuilding Industry Corporation... interesting combo there to say the least, probably something to do with a certain "big wave" and a certain "easterly wind"

Anyway, the paper talks about a new model for testing the elasticity of N15 under strain the Chinese team has developed, which is based on existing methodologies designed for HTPB-based solid propellants as their chemical compositions are the same/similar, and it references N15 as a HTPB propellant containing 70% solids in their tests.

Not a single mention of NEPE or other binders, nor would you expect them to as the chemical makeup would be different. This is as best of an English source with any authority that I could find.

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I never said N-15 is NEPE. But if as you said the difference of all these solid fuels are just binders, that means NEPE or PBAN aren't much different from HTPB either, just like N-15 isn't much different from HTPB, right? In other words, I can say that NEPE is just another HTPB?

Here is the N15 formula. There is no HTPB formula in the article. If as you said the difference is only the binders, without knowing HTPB's formula, how do you tell what N15 really is?

For comparison, I find the formula of Japan's SRB from

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describes the propellant as "HTPB/AP/Al=12/68/20", which means, proportioned by mass, HTPB plus curative 12% (binder and fuel),

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68% (oxidizer), and

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powder 20% (fuel).

The difference is lot of RDX in N-15, very low content of AP. What exotic compound could NEPE have to make it not just another HTPB? Please share the formula of NEPE and PBAN-ACP if you have, I'd like to read.

 

[taxiya]

Using the formula here

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,

the Specific Impulse comes out to be 383 which is way bit too high. Obviously, the 500-ton thrust is not all through the 115-second test.

Anyway, the rocket motor with a mass of just 150 tons proved to be very powerful, able to put out 500 tons of thrust.

SSSRB's thrust profile. Apparently it's 1500t thrust is the maximum. So the 500t here must only be its max. It is also logical to do so if the SRB is meant for practical usage.

 

[Helius]

This is how the Specific Impulse is defined:

For all vehicles, specific impulse (impulse per unit weight-on-Earth of propellant) in seconds can be defined by the following equation:

where:

• 
  is the thrust obtained from the engine (
  Please, Log in or Register to view URLs content!
  or
  Please, Log in or Register to view URLs content!
  ),
• 
  is the
  Please, Log in or Register to view URLs content!
  , which is nominally the gravity at Earth's surface (m/s2 or ft/s2),
• 
  is the specific impulse measured (seconds),
• 
  is the
  Please, Log in or Register to view URLs content!
  of the expended propellant (kg/s or
  Please, Log in or Register to view URLs content!
  /s)

Basically, I'm making an assumption of a constant fuel-burning rate and constant thrust.
Exhaust velocity can be calculated when the Isp is known.
.

I'm well aware of the formula(s/e). As I said, to get a rudimentary m-dot you're missing at least 2 metrics, namely the volume of the booster itself, which we don't know, and the density of the propellant, which we also don't know.

Burn time alone won't give you mass flow rate to infer specific impulse. So I'm not sure what assumptions you're placing on those two values to arrive at whatever mass flow rate you ended up with that then gave you a 383s Isp.

I never said N-15 is NEPE. But if as you said the difference of all these solid fuels are just binders, that means NEPE or PBAN aren't much different from HTPB either, just like N-15 isn't much different from HTPB, right? In other words, I can say that NEPE is just another HTPB?

They're different chemical mixtures. One is polybutadiene-based and the other is nitroglycerin-based. Why would you conflate them by saying they're the same?

Here is the N15 formula. There is no HTPB formula in the article. If as you said the difference is only the binders, without knowing HTPB's formula, how do you tell what N15 really is?
View attachment 100832
For comparison, I find the formula of Japan's SRB from

Please, Log in or Register to view URLs content!

Please, Log in or Register to view URLs content!

describes the propellant as "HTPB/AP/Al=12/68/20", which means, proportioned by mass, HTPB plus curative 12% (binder and fuel),

Please, Log in or Register to view URLs content!

68% (oxidizer), and

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powder 20% (fuel).

The difference is lot of RDX in N-15, very low content of AP. What exotic compound could NEPE have to make it not just another HTPB? Please share the formula of NEPE and PBAN-ACP if you have, I'd like to read.

The HTPB is in the "adhesive" category. It's the binding agent that 'binds' the solid fuel mixture i.e. AP, Al, RDX together in this instance.

We won't know the exact chemical composition of N15 if they don't advertise it (why would they?). To reiterate yet again, it's the binding process that defines which category the solid fuel falls under, because what actually makes the fuel burn has been predominantly the AP in the fuel mix. That hasn't changed in the decades solid fuel has been in use.

NEPE-75 isn't purely ammonium perchlorate either. A big chunk of its fuel mix is also allocated to Al (aluminium) and HMX (High Molecularly-weighted RDX).

 

[by78]

I think you mean have entered the Mengtian module.

It is amazing to see that the Chinese Space Station is now complete. I started following the program in 2011 after China got discriminated off the ISS and then they decided to build their own. And the plan was to complete it in around 10 years, which they have done even with some Long March 5 delays. That in itself is amazing and certainly deserves more recognition. Unfortunately the program receives almost no attention in the West. Everybody should definitely look out for 26-28 november when we will see 6 astronauts onboard at once!

Yes, I meant the Mengtian module.

 

[taxiya]

They're different chemical mixtures. One is polybutadiene-based and the other is nitroglycerin-based. Why would you conflate them by saying they're the same?

I did not say N-15 is the same as NEPE. Remember yourself pointed out what I said was only "equivalent performance".

As for N15, all I got from your quotes is that it having an "equivalent performance to NEPE" =/= it being NEPE.

What I said "In other words, I can say that NEPE is just another HTPB?" is what you think that I am conflating them being the same, but that is a question to you based on my understanding (I wasn't aware of the type of binders) of your post. Not that I was trying to assert.

To make myself clear, what kind of binder N-15 uses isn't my concern, but rather how you concluded that N-15 is HTPB type when we don't have source available.

The HTPB is in the "adhesive" category. It's the binding agent that 'binds' the solid fuel mixture i.e. AP, Al, RDX together in this instance.

We won't know the exact chemical composition of N15 if they don't advertise it (why would they?). To reiterate yet again, it's the binding process that defines which category the solid fuel falls under, because what actually makes the fuel burn has been predominantly the AP in the fuel mix. That hasn't changed in the decades solid fuel has been in use.

So we don't know the composition of N15, but you are somehow sure that N15 is HTPB (polybutadiene-based)? This is the root cause of my confusion of what you are saying.

Please quote the source and present me the chain connecting the dots that makes your assertion. I am feeling that we are walking around a circle now.

My understanding of the paper that you provided is that they based their development of the test methodology on their experience gained from testing HTPB propellent. The article does not say the N-15 is in HTPB category. The formular listed Plasticizer without saying what kind of binder it is.

NEPE-75 isn't purely ammonium perchlorate either. A big chunk of its fuel mix is also allocated to Al (aluminium) and HMX (High Molecularly-weighted RDX).

Having lots of RDX is similar to N15, I emphasize again, I am not saying N15 is nitroglycerin-based as NEPE, which is unknown to me for the moment and I need your source.

 

[Helius]

I did not say N-15 is the same as NEPE. Remember yourself pointed out what I said was only "equivalent performance".

What I said "In other words, I can say that NEPE is just another HTPB?" is what you think that I am conflating them being the same, but that is a question to you based on my understanding (which was wrong) of your post. Not that I was trying to assert.

This is starting to sound like a facetious argument. You said if they aren't that different then NEPE is just another HTPB.... But they are different, very different. So why would you put forward that line of questioning in the first place? What are you even arguing for...?

So we don't know the composition of N15, but you are somehow sure that N15 is HTPB (polybutadiene-based)?

Please quote the source and present me the chain connecting the dots that makes your assertion. I am feeling that we are walking around a circle now.

The whole paper deals with N15 as a HTPB fuel...

The "composition" is laid out in the formula you've also highlighted. Note the figures aren't exact percentages. What we don't know is what chemicals and the ratios of which are in the HTPB mixture.

To clarify in case you didn't know, hydroxyl-terminated polybutadiene isn't a single chemical. It's a mixture (hydroxyl, poly-), the polybutadiene itself is also a mixture that, again, gives the solids their elasticity so they can be cured, and that can be tweaked to give different properties to the solids it intends to mix with.

The same is true for the solids themselves as it can be richer in AP or less depending on how powerful you want your combustion and the duration of your burn.

Having lots of RDX is similar to N15, I emphasize again, I am not saying N15 is nitroglycerin-based as NEPE, which is unknown for the moment.

Yeah that's because it's what makes the rocket go. RDX is a propellant, NEPE isn't, neither is HTPB.

 

[gelgoog]

There are other explosives than RDX. I have heard people talking about possible use of CL-20 in solid rockets like a decade ago.

 

[taxiya]

This is starting to sound like a facetious argument. You said if they aren't that different then NEPE is just another HTPB.... But they are different, very different. So why would you put forward that line of questioning in the first place? What are you even arguing for...?

Because I honestly did not know the different type of binders.

The whole paper deals with N15 as a HTPB fuel...

The "composition" is laid out in the formula you've also highlighted. Note the figures aren't exact percentages. What we don't know is what chemicals and the ratios of which are in the HTPB mixture.

My last try, this is what I highlighted.


I see Adhesive and Plasticizer. Which one indicates that N15 is polybutadiene or nitroglycerin based? If I understand you right, the type decides whether it is a NEPE type or HTPB type, right?